Field of the invention

This invention relates to an inflow cannula for blind insertion of an intravascular blood pump, and more particularly to a cannula with a beveled tip which pushes the cannula to the center of the aortic valve for retrograde traversal.

Background of the invention

U.S. Patent No. 4,625,712 and copending application Serial No.129, 714 filed 12/07/87 disclose miniature high-speed blood pumps which can be threaded through a blood vessel to provide heart assist in emergency situations without major surgery. Typically, such pumps are inserted through, e.g., the femoral artery. An inflow cannula is positioned ahead of the pump during insertion, and this cannula must typically be pushed through the aortic valve in a retrograde direction.

In the past," such retrograde insertion was usually done by means of a wire guide over which the inflow cannula was slipped, and which was subsequently withdrawn. This method was unsatisfactory not only because it was awkward and carried a risk of injury to the vascular system and to the aortic valve, but also because it required the continuing observation of the wire during insertion by x-ray or other procedures. In an emergency, appropriate x-ray equipment may not be immediately available, and heart assist may have to be provided so quickly that the slow wire guide method may not be suitable.

A requirement therefore exists for an inflow cannula which can be attached to the intake of an intravascular blood pump and can be pushed ahead of the pump for blind retrograde . insertion into the left ventricle through the aortic valve without any additional apparatus and without danger of injury to the patient.

Summary of the invention

The present invention fulfills this requirement by providing a wire-reinforced silicon rubber cannula which has a spring-loaded curve built into it. This curve allows a reliable traverse of the aortic arch without getting the cannula caught in a major vessel such as, e.g., the left subclavian artery. The cannula of this invention carries at its leading end a soft, beveled tip which is so positioned with respect to the built-in curve that the tip tends to point inwardly of the curve.

As the soft, flexible tip approaches the aortic- valve, it contacts the sinuses of the valve on the inside of the arch and begins to fold upon itself. This action tends to push the body of the cannula," toward the center of the artery, and continued thrust of the cannula through the aorta causes the body of the cannula to penetrate through the aortic valve in an optimal position. After the cannula has entered the left ventricle, the flexible tip springs back to its original shape and allows blood to flow into the cannula without obstruction. Apertures are provided in the side of the cannula adjacent its leading end to prevent occlusion of the cannula intake by the flexible tip as a result of the pump's suction.

It is therefore the object of this invention to provide an inflow cannula for intravascular blood pumps which

is suitable for blind retrograde insertion into the left ventricle of the heart through the aortic valve without substantial risk of injury.

It is another object of the invention to accomplish this purpose by using a cannula with a spring-loaded curve and a soft, flexible tip which is beveled toward the inside of the curve and is capable of temporarily folding upon itself upon encountering the aortic valve so as to center the cannula for penetration through the aortic valve.

Brief description of the drawings

Fig. 1 is a schematic view illustrating the use of the invention in the arterial system of a patient;

Fig. 2 is a plan view of the cannula of this invention;

Fig. 3 is a side elevation of the tip of the cannula of Fig. 2; and

Figs . 4a through 4c are is a detail view of the centering and penetrating action of the cannula tip when it encounters and tranverses the aortic valve.

Description of the nreferrsd embodiment.

Fig. 1 shows, in schematic form, the environment in which the invention is used. When heart assist is needed in an emergency or for other medical reasons, a miniature intravascular blood pump 10 is percutaneously inserted into the femoral artery (not shown) and is pushed through the femoral artery into the aorta 12 . Rotary power for the cable drive 13 of pump 10 and purge fluid for its hydrostatic

bearings is supplied through a catheter 14 from outside the patient's body, as described in more detail in copending application Ser. No. filed . The cannula 16 of this . invention is attached to the forward (i.e. intake) end of the pump 10 and guides it through the patient's arterial system during insertion.

In order to assure a steady blood flow through .the pump 10, it is desirable to locate the blood intake in the left ventricle 17 of the heart; i.e. the leading end of the inflow cannula 16 must be passed through the aortic valve 18. This poses several problems, particularly in emergency situations where no x-ray equipment is readily available to track the insertion of the cannula 16. To begin with, the cannula 16 must follow the aortic arch 20 smoothly without getting caught in one of the major arteries 24 branching off from the aorta 12 in the arch 20. Next, the cannula 16 must be substantially centered in the aorta 13 as it approaches the aortic valve 18 so as not to get caught in or injure the sinuses 28 (Fig. 4a) while pushing aside the aortic leaflets 30. Finally, once the cannula 16 has passed through the aortic, valve 18, its inflow opening must be completely unobstructed. All of these procedures must, of course, be accomplished with minimal risk of injury to the patient's vascular system.

Figs . 2 and 3 show the inventive cannula structure which accomplishes these results. The cannula 16 is formed from a tube 32 of soft silicon rubber which, in its body- section 34, covers a spring 36. The tip section 38 of the cannula 16 beyond the leading end of spring 36 is beveled for a purpose described below. A radioopaque strip 40 may be interposed between the tube 32 and the spring 36, and extended to the leading end of the tip section 38, for x-ray tracking of the cannula insertion when x-ray equipment is available.

In accordance with one aspect of the invention,

conventional forming techniques are employed to bias the body section 34 of cannula 16 into the arcuate shape best illustrated in Fig. 2. This bias urges the cannula 16 to follow the curve of the aortic arch 20 upon insertion and keeps it away from the branch arteries while it traverses the aortic arch. Of course, the loading imposed by spring 36 is weak enough to allow the body section 34 to be straightened by the walls of the arteries when it traverses a straight section of artery.

On each end of its arcuate portion, the body section 34 has short straight portions 42,44. The trailing straight portion 42 may be attached to the intake end of pump 10 in any conventional manner, and the leading straight portion 44 allows the intake opening 46 to remain centered in the left ventricle 17 (Fig. 1) after traversing the aortic valve 18. As a general indication of the parameters of the cannula 16, its diameter may be on the order of 7 mm; the arcuate portion of the body section 34 may have a radius on the order of 2.5 cm; the straight portion 42 may be on the order of 10 cm long; and the straight portion 44 may have a length on the order of 4 mm, not counting the 4 cm-long tip section 38. As best shown in Fig. 3, the tip section 38 is beveled at about a 20° angle at its leading end/ A pair of auxiliary openings 48 are provided in the side of tip section 38 for a purpose discussed below.

Fig. 4b shows in more detail what happens as the tip section 38 contacts the aortic valve 18\when moving in the direction of rrow 49. The soft beveled end 50 of tip section 38 is not strong enough to penetrate or push aside the aortic leaflets 30; consequently, it resiliently collapses. In doing so, it follows the curve of the aortic leaflet 30 against which it has impinged until it is stopped by the wall of the aorta 13 at sinus 28. Once stopped, further collapse of the

beveled portion 50 of tip section 38 causes the body section 34 of cannula 16 to be pushed toward the center of the aorta 13. Continued insertion of the cannula 16 will therefore cause the cannula 16 to traverse the aortic valve 18 dead center, eliminating the risk of its getting caught in, and damaging., the sinus 28.

As the body section 34 of cannula 16 traverses the aortic valve 18, the soft beveled tip portion 50 folds over the intake opening 46 of cannula 16 and follows the leading end of the body section 34 into the left ventricle 17. As soon as the beveled tip portion 50 has passed entirely through the aortic valve 18, its resiliency causes it to spring back to is original shape where it leaves the intake opening 46 unobstructed (Fig. 4c) .

It is possible that the suction of pump 10 may hold, the collapsed beveled tip portion 50 against the intake opening 46 and prevent it from returning to its original shape. To avoid this problem, auxiliary openings 48 are provided in the side of the tip section 38. The auxiliary openings 48 provide a sufficient bypass flow path to allow the inherent resilience of the tip section 38 to overcome any suction force at the intake opening 46, even if the pump 10 is operating at maximum speed.

As illustrated in Fig. 3, the auxiliary openings 48 are preferably so positioned that their axes are parallel to the beveling plane of the beveled tip portion 50. In this manner, the beveled tip portion 50 is prevented from obstructing either auxiliary opening 48 during its passage through the aortic valve 18.

It will be seen that the present invention provides an inflow cannula for intravascular pumps which is suitable for rapid, blind retrograde insertion into the left ventricle of a human heart when immediate heart assist is called for in

emergencies or other situations.